Broadcast systems have embraced the demand for high quality transmissions made possible by digital technology. The digital revolution has transformed the delivery of broadband services, including audio and video programming as well as data transmission. Satellite communication systems have emerged as a viable solution for supporting such broadband services. As such, power and bandwidth efficient modulation and coding are highly desirable for satellite communications systems to provide reliable communication across noisy communication channels. In broadcast applications supported by such systems, continuous mode modems are widely used. Codes that perform well in low signal-to-noise (SNR) environments are at odds with these modems with respect to synchronization (e.g., carrier phase and carrier frequency).
Conventional digital broadcast systems require use of additional training symbols beyond that of the normal overhead bits in a frame structure for their synchronization processes. The increase in overhead is particularly required when low Signal-to-Noise (SNR) is low; such an environment is typical when high performance codes are used conjunction with high order modulation. Traditionally, continuous mode modems utilize a feedback control loop to acquire and track carrier frequency and phase. In this synchronization process, the FEC (Forward Error Correction) coded data fields, e.g., preambles of a block code, which contain known data symbols, are simply ignored. Such conventional approaches that are purely based on feedback control loops are prone to strong Radio Frequency (RF) phase noise and thermal noise, causing high cycle slip rates and an error floor on the overall receiver performance. Thus these approaches are burdened by increased overhead in terms of training symbols for certain performance target, in addition to limited acquisition range and long acquisition time. Further, these conventional synchronization techniques are dependent on the particular modulation scheme, thereby hindering flexibility in use of modulation schemes.
Therefore, there is a need for a digital communication system that provides synchronization immune to phase noise and thermal noise. There is also a need for a carrier synchronization approach that is simple to implement and incurs as few training symbols as possible. There is also a need to provide a synchronization technique that is flexible as to provide modulation independence.